If the TT could return the number of legal moves for EXACT/ALPHA positions, what could that information be used for?
What comes to mind is if we know there is only one move available, but not sure what to do with it.
Ideas?

NumberOfMoves = 0
get next move ()
{
if !legal()
continue
increment NumberOfMoves
// do stuff
}
if NumberOfMoves = 0, return mate or draw
// if we make it all the way through to here
// we have tried every move....
if we have a best move
store TT (EXACT, NumberOfMoves)
else
store TT(ALPHA, NumberOfMoves)

If the TT could return the number of legal moves for EXACT/ALPHA positions, what could that information be used for?
What comes to mind is if we know there is only one move available, but not sure what to do with it.
Ideas?

My first engine set a bit in a position's TT entry if the search had figured out there was only one legal move. That bit was then used to trigger an extension the next time the position was encountered.